Problems with millis()

Projects Programming
1

Hi,
I am having problems with this code. I am trying to make "smart car" library to help me with my upcomming school project. What I am trying to do is, When I am moving in certain direction, I want to check distance aswell (for distance measuring I am using HC-SR04 sensor), but something does't seem to work. If I comment out m_distance = m_sensor.GetDistance() than everything work just fine. I tested function GetDistance() and works as it should.

bool SmartCar::MoveForward_ForSetTime(const int delay_t, const float setDistance) 
{
	unisgned long timeNow = millis();
	while (millis() <= timeNow + delay_t)
	{
		//m_distance = m_sensor.GetDistance();
		//if (m_distance <= setDistance)
		//	return false;
		m_motors.moveForward(m_speed);
	}
	return true;
}
2

https://www.arduino.cc/en/Hacking/libraryTutorial

https://forum.arduino.cc/t/using-library-in-another-library/337306/4

3

The problem is not creating library.

Thank you for answer anyway.

4

Non-blocking timing tutorials:
Blink without delay().
Beginner's guide to millis().
Several things at a time.

1 Like
5

And what would be that something?

And what is the problem?

You could post your sketch and then say "I was expecting this, but instead I get that", or "getDistance() seems to be interfering with the movement of the motor and I don't know why"

Take a brief moment to read: https://forum.arduino.cc/t/how-to-get-the-best-out-of-this-forum/681310

6

This math will go wrong when the timer overflows. Use this instead:
while (millis() - timeNow <= delay_t)
Always subtract past time from the current time to get a time interval.

Note: It might make more sense to rename "timeNow" to "startTime since a moment after you set it, it is not the time "now" anymore.

1 Like
7

@schoolboy2 thanks to that while loop you have a disguised blocking code that may be causing havoc elsewhere. Unless there is something you know and we don't...

8

The while loop should be "blocking". The way I want to use this, is when I call my method MoveForward_ForSetTime(const int delay_t, const float setDistance) the motors shoud be moving in that direction for specified time, unless distance measured is less than given setDistance and in that case I want to terminate while loop.

9

You could print this to see why it never breaks your loop. Print the number you are comparing it to once also to see if you get a surprise there.

a7

10

I already did it and it's not a problem. If I comment if statement, the code still doesn't work. It looks like GetDistance() function is causing the problem in a while loop, but if I use GetDistance() function alone it works and I do not know what could be wrong with it, since it just creates a pulse with triger pin and recieve a pulse with echo pin and than covert travel time to distance and return that distance.

11

Time to post all your code or a small example that compiles, runs and illustrates the problem.

There is no reason that can be seen now for a function that works in one place and doesn’t work in another.

a7

12

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